1. Field of Invention
The present invention relates to an optical filter, an optical device, and a projector.
2. Description of Related Art
Related art projectors have been used in presentations and in home theaters. A related art projector enhances image quality. This projector includes a color separating optical device to separate light beams from a light source into a plurality of types of colored light beams; three light modulators, such as liquid crystal panels, to modulate each separated colored light beam in accordance with image information; a color synthesizing optical device, such as a prism, to synthesize the colored light beams modulated by the light modulators and allow the synthesized colored light beam to exit therefrom; and a projection optical system to enlarge and project the synthesized colored light beam.
Since such a projector is used by placing it on a desk or a table, to make viewing easier, the projector is constructed to perform what is called “tilting-and-shifting projection” in which a projection area is displaced slightly upward from the optical axis of the projection optical system. The “tilting-and-shifting projection” can be achieved by displacing the central axis of a light-beam-exiting end of the color synthesizing optical device downward, which is in a direction opposite to the tilting-and-shifting direction, from the optical axis of the projection optical system.
When a related projector is used as a data projector to project an image based on RGB signals from a computer, the related projector uses a light source having a spectrum with high luminance in the wavelength range of green light (500 nm to 570 nm) for the purpose of providing a sufficiently bright projected image.